At a meeting held at Langley Field on January 16 (attended by Drs. Dryden and Silverstein), it was decided to negotiate with McDonnell to design the capsule so that it can be fitted with either a beryllium heat sink or an ablation heat shield. It was further decided that McDonnell should supply  a specified number (of the order of eight) ablation shields and a specified number (of the order of six) beryllium heat sinks. It is anticipated that flights with both types of heat protection will be made . . . . In case of a recovery on land, the capsule with a beryllium heat sink will require cooling; this is accomplished by circulating air either between the heat sink and the pressure vessel, or by ventilating the pressure vessel after impact.17Regarding the escape system, McDonnell's proposal had carefully weighed the relative merits of STG's pylon, or tower, type of tractor rocket with the alternative idea, which used three sets of dual-pod pusher rockets, similar to JATO bottles, along either side of three fins at the base of the capsule. McDonnell chose the latter system for its design proposal, but the STG idea prevailed through the contract negotiations, because the Redstone was calculated to become aerodynamically unstable with the pod-type escape system, and the Atlas would likely be damaged by jettisoning the pod fins.18 The escape system for an aborted launch was intimately interrelated with the problems of the heatshield and of the normal, or nominal, landing plans. By mid-March Robert F. Thompson's detailed proposals for a water landing helped clarify the nature of the test programs to be conducted.
While McDonnell agreed to design the capsule so that it could be fitted alternatively with either a beryllium heat sink or an ablation heatshield, the prime contractor farmed the fabrication of these elements to three subcontractors: Brush Beryllium Company of Cleveland was to forge six heat-sink heatshields; General Electric Company and Cincinnati Testing and Research Laboratory (CTL) were to fabricate 12 ablation shields. The Space Task Group relied on Andre J. Meyer, Jr., to monitor this critical and sensitive problem, the solution to which would constitute the foremost technological secret in the specifications for the manned capsule.
Meyer, one of the original STG members from Lewis in Cleveland, had been commuting to Langley for 10 months. He soon discovered a bottleneck in the industrial availability of beryllium. Only two suppliers were found in this country; only one of these, Brush, had as yet successfully forged ingots of acceptable purity. But ablation technology was equally primitive, so plans had to be made on dual tracks. Meyer had had much experience with laminated plastics for aircraft structures. He had previously learned, in consultations with the Cincinnati Testing Laboratory, how to design a "shingle layup" for fabrication of an ablation heatshield. While collecting all available information on both the ablative plastic and the beryllium industries, Meyer listened to the Big Joe project engineers, Aleck C. Bond and Edison M. Fields. They argued for ablation, specifically for a fiber glass-phenolic material, as the primary heat protection for the astronaut. Before moving to Virginia in February, Meyer consulted on weekends with Brush Beryllium in Cleveland, watching its pioneering progress in forging ever larger spherical sections of the exotic metal, which is closely akin to the precious gem emerald. But Meyer, along with Bond and Fields, grew more skeptical  of the elegant theoretical deductions that supported the case for beryllium. Mercury would have a shallow angle of entry and consequently a long heat duration and high total heat; they worried about the possibility that any heat sink might "pressure cook" the occupant of the capsule. So Meyer, using CTL's shingle concept, perfected his designs for an ablative shield.19
There was something basically appealing about the less tidy ablation principle, something related to a basic principle in physics, where the heat necessary to change the state (from solid to liquid to gas) of a material is vastly greater than the heat absorbed by that material in raising its temperature by degrees. Meyer became convinced by March that beryllium would be twice as expensive and only half as safe. Consequently, Meyer and Fields concentrated their efforts on proving their well-grounded intuition that ablation technology could be brought to a workable state before the Big Joe shot in early summer.20
While lively technical discussions over ablation versus heat sink continued through the spring, the fact that Mercury officials had committed Big Joe to the proof-testing of an ablative shield also rather effectively squelched any further attempts at scientific comparisons. Whereas in January Paul E. Purser recorded that "we will procure both ablation and beryllium shields . . . and neither will be 'backup,' they will be 'alternates,' " by the end of April technological difficulties in manufacturing the prototype ablation shields became so acute as to monopolize the attention of cognizant STG engineers.21
Glennan and Silverstein in Headquarters therefore directed continuation of the heat sink development as insurance, while STG gradually consigned the alternative beryllium shield to the role of substitute even before the fiber glass phenolic shield had proved its worth. By mid-year of 1959, apparently only the Brush Beryllium Company still felt confident that the metallic heat sponge was a viable alternative to the glass heat vaporizer in protecting the man in space from the fate of a meteor. The complicated glass-cloth fabricating and curing problems for the ablation shield were mostly conquered by July. John H. Winter, the heatshield project coordinator at the Cincinnati Testing Laboratory, delivered his first ablation shield to NASA in Cleveland on June 22 under heavy guard.22
The critical question of whether to jettison the heatshield was active early in 1959. If the shield were a heat sink, it would be so hot by the time it reached the lower atmosphere that to retain it after the main parachute had deployed would be hazardous to the pilot. Also in case of a dry landing such a hot sponge could easily start a prairie or forest fire. On the other hand, a detachable shield would add complexity to the system and increase the risk of its loss before performing its reentry job. In one of the early airdrops a jettisoned shield actually went into "a falling leaf pattern after detachment. It glided back and collided with the capsule, presenting an obvious potential hazard for the pilot in his vehicle late in the reentry cycle."23 This incident prompted the decision that the heatshield would be retained, although it might very well be lowered in the final moments of the flight if it could help attenuate impact. The memory of this early collision  after jettisoning continued to haunt STG engineers until they rejected the beryllium heat-sink shield altogether.
Although the heatshield problem was highly debatable at the inception of the project, there was consolation in the fact that at least two major development areas were virtually complete. The two items considered frozen at the end of January 1959 were the external configuration of the capsule, except for the antenna section, and the form-fitting couch in which the astronaut would be able to endure a force of 20 g or more, if it should come to that.24 The Space Task Group was pleased to have something as accomplished fact when so many other areas were still full of uncertainties.
To George Low's ninth weekly status report for Administrator Glennan on STG's progress and plans for Project Mercury was appended a tabular flight test schedule that summarized the program and mission planning as envisioned in mid-March 1959. Five Little Joe flights, eight Redstone, two Jupiter, ten Atlas flights, and two balloon ascents were scheduled, the categories overlapping each other from July 1959 through January 1961. The first manned ballistic suborbital flight was designated Mercury-Redstone flight No. 3, or simply "MR-3," to be launched about April 26, 1960. And the first manned orbital flight, designated Mercury-Atlas No. 7, or "MA-7," was targeted for September 1, 1960. After that, STG hoped to fly several more, progressively longer orbital missions, leading finally to 18 orbits or a full day for man in space. Although merely a possible flight test plan, this schedule set a superhuman pace and formed the basis for NASA's earliest expectations.25
17 Low, "Status Report No. 5," Jan. 20, 1959. Cf. Low, "Status Report No. 3," Dec. 27, 1958.
18 "Status Report No. 5"; Manned Satellite Proposal, Vol. II: Technical Proposal, 10.
19 Andre J. Meyer, Jr., interview, Houston, Feb. 24, 1964, and comments, Sept. 1, 1965; Ms., Meyer for Project Mercury Technical History Program, "Mercury Heat Shield History," June 1963, regards the beryllium alternative as only a secondary solution from the beginning.
20 Edison M. Fields, interview, Houston, June 18, 1964; Aleck C. Bond, interview, Houston, March 13, 1964.
21 Purser, log for Gilruth, Jan. 14, 1959. Cf. "Specifications for Manned Spacecraft Capsule." Memos, Fields to Chief, Flight Systems Div., "Visit to B. F. Goodrich Concerning Ablation Heat Shield for HS-24," April 20, 1959; and "Visit to C.T.L. Concerning Ablation Heat Shields for HS-24," April 21, 1959. General Electric Co. (Missile and Space Vehicle Dept., Philadelphia) had found it necessary to subcontract the large-scale development of its design process to the B. F. Goodrich Co., Akron. Big Joe flew a Goodrich heatshield.
22 "Specification for Ablation Heat Shield," STG Specification No. S-19-B, April 28, 1959, a five-page revision by Fields of Specification No. S-19A, March 2, 1959. See also "Beryllium in Project Mercury," brochure, Brush Beryllium Co., undated [about June 1959]. For the techniques of ablation shield manufacture, see "Development of Reinforced Plastic Materials and Fabrication Procedures for Reentry Protection Shield for Capsule, Project Mercury," Cincinnati Testing and Research Laboratory, Reports Nos. 1 and 2 (final), May 1 and July 1, 1959.
23 "How Mercury Capsule Design Evolved," Aviation Week, LXX (Sept. 21, 1959), 57.
24 "Project Mercury Status Report No. 1 for Period Ending Jan. 31, 1959," STG/Langley Research Center, 2, 26. See also Ms. paper, Marvin S. Hochberg, "Design and Fabrication of the Project Mercury Astronaut Couch," an undated and unnumbered McDonnell Aircraft Corp. report received by STG June 20, 1963.
25 Low, "Status Report No. 9 - Project Mercury," March 21, 1959, 6. On this chart MA-1 stood for the flight that later became known as Big Joe. Hence all flights in the Atlas series dropped in numerical sequence; MA-7 became MA-6, but remained the first planned manned orbital flight.